Dishes used for baking and other cooking applications typically are equipped with a cover so that the foodstuffs within the dish can be covered while being cooked. Covered cooking helps retain heat and moisture within the dish and may otherwise aid the cooking process. Even if covered cooking is not desired the cover can be used while serving to help keep the contents of the dish warm. The term "dish" is used in a general sense to mean ovenware such as a casserole dish suitable for use in an oven such as a microwave oven or a conventional oven. The term "dish" would also include a cooking utensil intended for use on a range-top cooking element.
For some cooking applications, it would be advantageous to provide an opening in the otherwise covered dish to allow carefully controlled amounts of steam or other vapors to escape. Further, while it may be desirable to keep a dish covered during cooking, it is nevertheless frequently desirable to gain access to the interior of the dish during cooking. For example, it may be convenient to insert a cooking thermometer into the dish without completely removing the cover. While serving it may be convenient to leave a serving spoon in the dish and yet keep the dish covered.
With some cooking dishes of the prior art, one must substantially remove the entire cover or lid in order to gain access to the interior of the dish. This is at best awkward, because the cook must either hold the removed lid in one hand or else must find a clean and heat-safe location on which the hot lid can temporarily rest. Moreover, removing the lid from a hot container carries the risk that the cook may be burned by the sudden and uncontrolled escape of steam from the container.
To need to provide an opening for venting steam from the dish or inserting a cooking thermometer may be met through the expedient of setting the lid ajar on the dish. This solution is awkward and usually difficult to regulate, and is undesirable. Another prior art venting expedient, usually limited to metal lids for saucepans or the like, requires a separate butterfly valve element movably attached to the cover. Such valves are not adjustable, easily become clogged, are relatively costly and in any case are not readily adaptable to ceramic or glass cookware such as bowls. Other prior art dishes have located a venting arrangement in the handle of the dish so that the escape of steam can cause a problem for a person handling the container. Locating the vent in such a fashion increases the likelihood that steam will condense on the handle making it hot or slippery or both.